The teen-party movie has been a multiplex staple for the last three decades. Project X seems to have little ambition beyond providing a version that's a bit more over-the-top. A harmless enough venture, you might think. Meant to be a bit shocking, perhaps. Well, it is indeed shocking, but not in the way you might expect.

When it comes to hardcore debauchery, a surprising degree of restraint is observed. There's little in the way of sex in Project X, let alone orgiastic abandon. Body fluids are hardly in evidence; Bridesmaids made a much better fist of defecation and projectile vomiting. Signs warn party-goers that nudity is compulsory, yet the girls are allowed to keep their knickers on. What is, however, startling is the nastiness of the attitudes in play. (Spoilers ahead.)

The boys refer to their female classmates as "hos" and "bitches" and seek their company only as masturbatory aids. The girls eagerly endorse their own abuse. They're all good looking, but that may be because the invite included the injunction: "Ugly bitches stay home." A dwarf gets locked in the oven, while a pet dog is tied to helium balloons and sent aloft. A neighbour who complains about the noise is simply Tasered.

The proceedings are oddly joyless. There's none of the charm, warmth, wit or remorse to be found in other party films. The drug-fuelled revelry seems desperate rather than rapturous. Thomas, the 17-year-old host, isn't really staging the event to celebrate his birthday or even to have fun; he is out to persuade his schoolmates that he's cool, and therefore merits pussy. The suffering inflicted in the process, both on his own family and the entire neighbourhood, is acceptable collateral damage. All that matters is the grim pursuit of personal advantage.

It works. The mayhem that Thomas precipitates earns him the respect he craves. His college fund will have to be spent on rebuilding the family home, and the law is on his tail. No matter: at school he is now a superhero. So he gets the girl he wants, reassuring her that he doesn't care about having bankrupted his parents because he cares about her instead.

It's not only Thomas's peer group that applauds him. He wins the attention of the media, and with it celebrity status. Before the party, his dad declared him "a loser". As that same dad surveys the wreckage of his family's life, he ventures wonderingly: "I didn't know you had it in you."

You can't say this film lacks a moral. If you're young, you're entitled. So just do what it takes to get what you want. Whatever price you and others have to pay, it will be worth it. In the end, everyone will approve, including the grownups. Thank you for bringing this to our attention, Warner Bros.

Hollywood is terrified that it is losing its grip on the young male audience on which its success has depended for so long. Project X could be interpreted as a fantasy concocted to appease a generation mistakenly feared by ageing film-makers. Yet the film's producer, Todd Phillips, declares: "The whole movie really rests on authenticity." Might it contain an element of truth?

Young people have always sought out festivals of misrule, but the out-of-control teenage house-party is a product of our age. It's not just that smartphones and social media have made it easier for gatecrashers to mobilise. The relationship between adolescents and their parents has also changed.

Teenagers want more and expect to get it. In the past, parents might have resisted misplaced demands, but many have lost the confidence to do so. They want to be liked, not respected, and their authority has therefore waned. Ordered out of the house because their children want to party, they may meekly acquiesce.

When it comes to partying, as in other fields, the young are allowed more autonomy; but are given less guidance on how they should exercise it. Like Thomas, they fall prey to the apparent imperatives of the moment. It's their parents' job to set them straight. Like Thomas's dad, they often don't.

Life isn't yet a wild party that applauds those who pursue their desires at everyone else's expense. Project X may be warning us that it is heading that way. At the screening I attended, young film-goers whooped excitedly at the dismal shenanigans depicted. Fair enough. Less heartening were the apparent beams of approval from the older people among them.

Presumably, they wanted to get down with the kids. But when it's bad down there, the kids need us to drag them out of it, not to provide them with our blessing. You can't blame Thomas. You can blame Thomas's dad.